: any of a genus (Trichogramma) of minute chalcid wasps that are parasitic as larvae in the eggs of other insects and are used in the biological control of lepidopteran pests
borrowed from New Latin Trichogramma, genus name, from tricho-tricho- + Late Latin gramma, a measure of weight (1/24 of an ounce) — more at gram entry 2
The genus name was introduced by the English entomologist John O. Westwood (1809-93) in "Descriptions of several new British Forms amongst the Parasitic Hymenopterous Insects," London and Edinburgh Philosophical Magazine and Journal of Science, vol. 2 (January-June, 1833), p. 444. Presumably the name is to be taken as "something the weight of a hair," though Westwood leaves no comment on its origin.